The present invention relates to an antenna, and in particular to an antenna with a uniform half-space radiation pattern.
As wireless local area networks (WLANs) proliferate, wireless networking is more popular. Access point antennas are, thus, highly valued. For WLAN access-point applications in different operation environments, various radiation patterns in the horizontal (azimuthal) plane, such as an omnidirectional radiation pattern or a half-space radiation pattern in one direction, are required for the mounting antennas.
For omnidirectional radiation, a monopole antenna is preferable. For half-space radiation, however, an additional metal reflector with a particular shape is added to the monopole antenna structure. US patent application publication No. 2002/0158807 A1 discloses a cylindrical metal reflector device with a specific opening for adjusting the radiation pattern of a monopole antenna, thereby creating the half-space radiation pattern. Such a structure (one monopole antenna and a reflector with a particular shape) is, however, oversized and complicated.
European patent No. 1,130,677 discloses a patch antenna comprising a patch element disposed above a flat ground plane. By adjusting an additional metal reflector cooperated with the ground plane, the radiation beam width, of 180° for uniform half-space radiation, can be enlarged. However, the radiation beam width of the patch antenna, however, can only reach 110°.
Japan patent No. JP2002-368532 discloses a microstrip antenna having a bulged ground plane and a lens-like structure formed by dielectric material to improve the radiation characteristics at low elevation. The improvement of the radiation beam width is, however, still non-obvious.
Japan patent No. JP2000-040917 discloses a cylindrical antenna provided with a circular radiating member and a circular ground plane. Such an antenna has a complicated structure and offers only limited improvement in enlarging the radiation beam width.